FT. MEADE, Md.—Bradley Manning’s former Army supervisor described on Wednesday a chaotic night shift work environment in Iraq where they were required to collect and analyze highly classified intelligence data to support the U.S. war against insurgents, but also often joined others casually listening to music, watching movies and playing video games on their computer screens.

Yet at the same time, Jihrleah Showman, an Army specialist who was Manning’s team leader, acknowledged that the young private first class was known in the intelligence unit as a highly competent computer whiz who could easily get around secret passwords to retrieve information about enemy combat cells.

Indeed, Showman testified in Manning’s court-martial here, the 25-year-old was so well-versed in computers that he told her he had completely “scrubbed” clean his personal desk- and laptop computers before joining the military, or otherwise he never would have been accepted into the Army.

“He indicated to me he was very fluent in computers, that he spoke their language, and that there was nothing he could not do on a computer,” she said.

But beyond the often nerdy life of a computer expert, the 25-year-old Manning also displayed a much lighter side. “He talked about social issues,” she said. “He talked a lot about liking to attend martini parties in the Washington area and having a lot of friends. And how he loved shopping and, before he joined the military, working as a barista at Starbucks.”

He also, she said, liked to debate U.S. policy. He was “very political,” she said, on the “extreme Democratic side.”

Manning is on trial for 21 charges of illegally downloading and transferring some 700,000 secret reports, videos and State Department cables to the anti-secrecy website WikiLeaks. If convicted this summer, he could be sentenced to life in prison.

Earlier this year, he pleaded guilty to 10 lesser charges of mishandling classified information, and for that could be sentenced to 20 years in prison.